In Exchange 2007 SP2 when at least two Entourage EWS (13.0.7) clients are open and connected to the same mailbox, replied to messages sometimes come back as unread.
The scenario tested is 40-60 messages replied to back to back, around the 30th or 40th e-mail messages will go from replied (read status) to replied (unread status). OWA marks the message as unread first and then sync to Entourage EWS. This does not happen when only one Entourage EWS client is connected and open for a individual's mailbox. This does not happen with WebDav.
Since we do not want to promote downgrading and Exchange 2010 will not support WebDav